docs: def intersperse(x, ys):
      """
      Returns an iterable where ``x`` is inserted between
      each element of ``ys``
  
      :type ys: Iterable
      """
      it = iter(ys)
  
      try:
          y = next(it)
      except StopIteration:
          return
  
      yield y
  
      for y in it:
          yield x
          yield y